A dream about an eruption signifies that your mental state is unstable.
An eruption in a dream also means that you are facing an emotional outburst from your subconscious mind. This scenario is usually associated with anger, aggression and frustration. There could be an argument in your dream as well.
The explosion of emotions is a sign that you are experiencing an emotional situation and should not be taken lightly. It is a warning that you need to be aware of and preferably put things in perspective before reacting. Take your time to allow the eruption to settle down, you will be able to see more clearly to handle yourself in a more controlled manner.